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1.
Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) was irradiated by 60Co γ‐rays (doses of 50, 100 and 200 kGy) under vacuum. The thermal analysis of control and irradiated PHBV, under vacuum was carried out by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile properties of control and irradiated PHBV were examined by using an Instron tensile testing machine. In the thermal degradation of control and irradiated PHBV, a one‐step weight loss was observed. The derivative thermogravimetric curves of control and irradiated PHBV confirmed only one weight‐loss step change. The onset degradation temperature (To) and the temperature of maximum weight‐loss rate (Tp) of control and irradiated PHBV were in line with the heating rate (°C min?1). To and TP of PHBV decreased with increasing radiation dose at the same heating rate. The DSC results showed that 60Co γ‐radiation significantly affected the thermal properties of PHBV. With increasing radiation dose, the melting temperature (Tm) of PHBV shifted to a lower value, due to the decrease in crystal size. The tensile strength and fracture strain of the irradiated PHBV decreased, hence indicating an increased brittleness. Copyright © 2004 Society of Chemical Industry 相似文献
2.
Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with 12 mol% hydroxyvalerate (HV) content and epoxidized natural rubber (ENR) with 50 mol% epoxidation
level were studied along with the thermal properties and morphologies. Glass transition temperatures reveal immiscibility
of the polymers over the entire composition range. The equilibrium melting point (T
m0) of PHBV in blends was determined applying Hoffman–Weeks step-wise annealing procedure. There is no significant variation
of T
m0 for PHBV with blend composition. Also the crystallinity of PHBV stays approximately constant in the blends, only a slight
decrease might be recognized with increasing ENR content. The rate of crystallization of PHBV decreases with PHBV content
according to a power law. Morphological studies by polarizing optical microscopy reveal a fine intraspherulitic dispersion
of ENR in volume-filling PHBV spherulites, which develop during isothermal crystallization. 相似文献
3.
Two series of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) triblock copolymers were prepared by the ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) and dibutylmagnesium in 1,4‐dioxane solution at 70°C. The triblock structure and molecular weight of the copolymers were analyzed and confirmed by 1H NMR, 13C NMR, FTIR, and gel permeation chromatography. The crystallization and thermal properties of the copolymers were investigated by wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results illustrated that the crystallization and melting behaviors of the copolymers were depended on the copolymer composition and the relative length of each block in copolymers. Crystallization exothermal peaks (Tc) and melting endothermic peaks (Tm) of PEG block were significantly influenced by the relative length of PCL blocks, due to the hindrance of the lateral PCL blocks. With increasing of the length of PCL blocks, the diffraction and the melting peak of PEG block disappeared gradually in the WAXD patterns and DSC curves, respectively. In contrast, the crystallization of PCL blocks was not suppressed by the middle PEG block. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
4.
Poly(N‐vinylpyrrolidone) (PVP) groups were grafted onto poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) backbone to modify the properties of PHBV and synthesize a new novel biocompatible graft copolymer. The effect of graft modification with PVP on the thermal and mechanical properties of PHBV was investigated. The thermal stability of grafted PHBV was remarkably improved while the melting temperature (Tm) was almost not affected by graft modification. The isothermal crystallization behavior of samples was observed by polarized optical microscopy and the results showed that the spherulitic radial growth rates (G) of grafted PHBV at the same crystallization temperature (Tc) decreased with increasing graft yield (graft%) of samples. Analysis of isothermal crystallization kinetics showed that both the surface free energy (σe) and the work of chain‐folding per molecular fold (q) of grafted PHBV increased with increasing graft%, implying that the chains of grafted PHBV are less flexible than ungrafted PHBV. This conclusion was in agreement with the mechanical testing results. The Young's modulus of grafted PHBV increased while the elongation decreased with increasing graft%. The hydrophilicity of polymer films was also investigated by the water contact angle measurement and the results revealed that the hydrophilicity of grafted PHBV was enhanced. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
5.
Various problems, including high crystallinity, high melting temperature, poor thermal stability, hydrophobicity and brittleness, have impeded many practical applications of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV) as an environmentally friendly material and biomedical material. In the work reported here, multi‐block copolymers containing PHBV and poly(ethylene glycol) (PHBV‐b‐PEG) were synthesized with telechelic hydroxylated PHBV as a hard and hydrophobic segment, PEG as a soft and hydrophilic segment and 1,6‐hexamethylene diisocyanate as a coupling reagent to solve the problems mentioned above. PHBV and PEG blocks in PHBV‐b‐PEG formed separate crystalline phases with lower crystallinity levels and lower melting temperatures than those of phases formed in the precursors. The crystallite dimensions of the two blocks in PHBV‐b‐PEG were smaller than those of the corresponding precursors. Compared to values for the original PHBV, the maximum decomposition temperature of the PHBV block in PHBV‐b‐PEG was 16.0 °C higher and the water contact angle was 9° lower. In addition, the elongation at break was 2.8% for a pure PHBV fiber but 20.9% for a PHBV/PHBV‐b‐PEG fiber with a PHBV‐b‐PEG content of 30%. PHBV‐b‐PEGs can overcome some of the disadvantages of pure PHBV; it is possible that PHBV might be a good candidate for the formulation of environmentally friendly materials and biomedical materials. Copyright © 2010 Society of Chemical Industry 相似文献
6.
Poly(3‐hydroxy octanoate) (PHO), poly(3‐hydroxy butyrate‐co‐3‐hydroxyvalerate) (PHBV), and linoleic acid were grafted onto chitosan via condensation reactions between carboxylic acids and amine groups. Unreacted PHAs and linoleic acid were eliminated via chloroform extraction and for elimination of unreacted chitosan were used 2 wt % of HOAc solution. The pure chitosan graft copolymers were isolated and then characterized by FTIR, 13C‐NMR (in solid state), DSC, and TGA. Microbial polyester percentage grafted onto chitosan backbone was varying from 7 to 52 wt % as a function of molecular weight of PHAs, namely as a function of steric effect. Solubility tests were also performed. Graft copolymers were soluble, partially soluble or insoluble in 2 wt % of HOAc depending on the amount of free primary amine groups on chitosan backbone or degree of grafting percent. Thermal analysis of PHO‐g‐Chitosan graft copolymers indicated that the plastizer effect of PHO by means that they showed melting transitions Tms at 80, 100, and 113°C or a broad Tms between 60.5–124.5°C and 75–125°C while pure chitosan showed a sharp Tm at 123°C. In comparison of the solubility and thermal properties of graft copolymers, linoleic acid derivatives of chitosan were used. Thus, the grafting of poly(3‐hydroxyalkanoate) and linoleic acid onto chitosan decrease the thermal stability of chitosan backbone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:81–89, 2007 相似文献
7.
Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (Tg). melting points (Tm) and crystallisation temperatures (Tc) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in Tg, Tm and Tc. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation. 相似文献
8.
A generalized equation was derived to calculate the melting temperatures of homopolymers and copolymers. The Gibbs‐Thomson equation for homopolymers and a modified application to copolymers were derived using the proposed equation. The melting temperature Tm0 in the Flory equation corresponds to the melting temperature TmC,∞ of copolymer crystals with stems of infinite length. Also, TmC,n*, the melting temperature for copolymer crystals with stems containing the maximum possible number of structural units, n*, should be used instead of Tm0 as the basis of supercooling in crystallization. The proposed equation shows good agreement with experimental data for α‐alkene‐ethylene homogeneous copolymers. 相似文献
9.
This study reports the synthesis of polyurethane–imide (PU–imide) copolymers using 4,4′-diphenylmethane diisocyanate (MDI) polytetramethylene glycols (PTMGs) and different aromatic dianhydrides. Differential scanning calorimetry (DSC) results indicate that PU–imide copolymers had two phase structures containing four transition temperatures (Tgs, Tms, Tgh and Tmh). However, only PU–imide copolymers were formed by soft PTMG(2000) segments possessing a Tms (melting point of soft segment). When different aromatic dianhydrides were introduced into the backbone chain of the polyurethane, although the Tgs (glass transition temperature of the soft segment) of some of PU–imide copolymers did not change, the copolymers with long soft segments had low Tgs values. The Tgh (glass transition temperature of hard segment) values of PU–imide copolymers were higher than that of polyurethane (PU). In addition, the high hard segment content of PU–imide copolymer series also had an obvious Tmh (melting point of hard segment). According to thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA), the PU–imide copolymers had at least two stages of degradation. Although the Tdi (initial temperature of degradation) depended on the hard segment content and the composition of hard segment, the different soft segment lengths did not obviously influence the Tdi. However, PU–imide copolymers with a longer soft segment had a higher thermal stability in the degradation temperature range of middle weight loss (about Td 5%–50%). However, beyond Td 50% (50% weight loss at temperature of degradation), the temperature of degradation of PU–imide copolymers increased with increasing hard segment content. Mechanical properties revealed that the modulus and tensile strength of PU–imide copolymers surpassed those of PU. Wide angle X-ray diffraction patterns demonstrated that PU–imide copolymers are crystallizable. © 1999 Society of Chemical Industry 相似文献
10.
Yong Tang Jia Hak Yong Kim Jian Gong Duok Rae Lee Bin Ding Narayan Bhattarai 《Polymer International》2004,53(3):312-319
This paper describes the synthesis of a series of ABA‐type triblock copolymers of trimethylene carbonate and ?‐caprolactone with various molar ratios and analyses the thermal and mechanical properties of the resulting copolymers. The structures of the triblock copolymers were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, FT‐IR spectroscopy and gel permeation chromatography. Results obtained from the various characterization methods proves the successful synthesis of block copolymers of trimethylene carbonate and ?‐caprolactone. The thermal properties of the block copolymers were investigated by differential scanning calorimetry. The Tm and ΔHm values of the copolymers decrease with increasing content of trimethylene carbonate units. Two Tgs were found in the copolymers. Furthermore, both of the Tg values increased with increasing content of trimethylene carbonate units. The mechanical properties of the resulting copolymers were studied by using a tensile tester. The results indicated that the mechanical properties of the block copolymers are related to the molar ratio of trimethylene carbonate and ?‐caprolactone in the copolymers, as well as the molecular weights of the resulting copolymers. The block copolymer with a molar composition of 50/50 possessed the highest tensile stress at maximum and modulus of elasticity. Block copolymers possessing different properties could be obtained by adjusting the copolymer compositions. Copyright © 2004 Society of Chemical Industry 相似文献
11.
This article describes a study on thermal behavior of poly(vinylidene fluoride‐chlorotrifluoroetheylene) [poly(VDF‐CTFE)] copolymers as polymeric binders of specific interest for high energy materials (HEMs) composites by thermal analytical techniques. The non‐isothermal thermogravimetry (TG) for poly (VDF‐CTFE) copolymers was recorded in air and N2 atmospheres. The results of TG thermograms show that poly(VDF‐CTFE) copolymers get degrade at lower temperature when in air than in N2 atmosphere. In the derivative curve, there was single maximum degradation peak (Tmax) indicating one‐stage degradation of poly(VDF‐CTFE) copolymers for all the samples. The other thermal properties such as glass transition temperature (Tg) and degradation temperature (Td) for poly(VDF‐CTFE) copolymers were measured by employing differential scanning calorimeter (DSC) technique. The kinetic parameters related to thermal degradation of poly(VDF‐CTFE) copolymers were investigated through non‐isothermal Kissinger kinetic method using DSC method. The activation energies for thermal degradation of poly(VDF‐CTFE) copolymers were found in a range of 218–278 kJ/mol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
12.
Poly(butylene terephthalate), poly(butylene azelate), and poly(butylene terephthalate/butylene azelate) random copolymers of various compositions were synthesized in bulk using the well‐known two‐stage polycondensation procedure, and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. As far as the thermal stability is concerned, it was found to be rather similar for all copolymers and homopolymers investigated. All the copolymers were found to be partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. Flory's equation was found to describe the Tm–composition data and permitted to calculate the melting temperatures (T°m ) and the heats of fusion (ΔHu) of both the completely crystalline homopolymers. Owing to the high crystallization rate, the glass transition was observable only for the copolymers containing from 30 to 70 mol % of the terephthalate units; even though the samples cannot be frozen in a completely amorphous state, the data obtained confirmed that the introduction of the aromatic units gave rise to an increase of Tg, due to a chain stiffening. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2694–2702, 1999 相似文献
13.
Liuchun Zheng Chuncheng Li Dong Zhang Guohu Guan Yaonan Xiao Dujing Wang 《Polymer International》2011,60(4):666-675
In this exploration of novel biodegradable polyesters, multiblock copolymers based on poly(butylene succinate) (PBS) and poly(1,2‐propylene terephthalate) (PPT) were successfully synthesized with hexamethylene diisocyanate as a chain extender. The amorphous and rigid PPT segment was chosen to modify PBS. The structures of the polymers were characterized using 1H NMR and 13C NMR spectroscopy, gel permeation chromatography and wide‐angle X‐ray diffraction; the physical properties were investigated using thermogravimetric analysis, differential scanning calorimetry, mechanical testing and enzymatic degradation. The results indicate that the copolymers possess satisfactory mechanical and thermal properties, with impact strength 186% higher than that of PBS homopolymer, while tensile strength, flexural strength, thermal stability and melting point (Tm) are slightly decreased. Crystallization and biodegradation rates are still acceptable at 5 wt% PPT, although they are decreased by the introduction of PPT. The addition of appropriate amounts of PPT can improve the impact strength effectively without an obviously deleterious effect on tensile strength, flexural strength, thermal stability, Tm, crystallization rate and biodegradability. This study describes a convenient route to novel multiblock copolymers comprising crystallizable aliphatic and amorphous aromatic polyesters, which are promising for commercialization as biodegradable materials. Copyright © 2011 Society of Chemical Industry 相似文献
14.
Rachele Pucciariello 《应用聚合物科学杂志》1996,59(8):1227-1235
The melting behavior of the alternating copolymer of ethylene and tetrafluoroethylene (ETFE) was investigated by differential scanning calorimetry (DSC). A complex melting pattern is observed, strongly influenced by the thermal history. Three melting processes can be identified, whose heats of fusion and peak temperatures (Tm1′, Tm1, and Tm2 at increasing values) strongly depend upon thermal treatments. The higher-temperature melting peak Tm2 is not affected by the crystallization conditions (i.e., cooling rate and annealing); therefore, it can be attributed to more perfect crys+als present in the original sample. The peak at Tm1 increases when the cooling rate is decreased and upon prolonged and/or higher-temperature annealing, and it fastly merges to the higher-temperature peak at Tm2. The peak at Tm1 can be due to crystals that are able to recrystallize and perfect during thermal treatments. Lastly, the peak at the lowest-temperature Tm1′, produced only by annealing and strongly developing on increasing annealing time and temperature, is the so-called annealing peak that can be attributed to much poorer crystallites grown among the larger ones. The melting behavior of ETFE is compared with that of the ethylenechlorotrifluoroethylene (ECTFE) alternating copolymer. © 1996 John Wiley & Sons, Inc. 相似文献
15.
Wei Hu Baijun Liu Dong Wang Yanhua Yang Chunhai Chen Zhenhua Jiang Wanjin Zhang Zhongwen Wu 《应用聚合物科学杂志》2003,89(5):1347-1350
Novel aromatic poly(ether ketones) containing bulky lateral groups were synthesized via nucleophilic substitution reactions of 4,4′‐biphenol and (4‐chloro‐3‐trifluoromethyl)phenylhydroquinone (CF‐PH) with 1,4‐bis(p‐fluorobenzoyl)benzene. The copolymers were characterized by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, and polarized light microscopy observation. Thermotropic liquid‐crystalline behavior was observed in the copolymers containing 40, 50, 60, and 70 mol % CF‐PH. The crystalline–liquid‐crystalline transition [melting temperature (Tm)] and the liquid‐crystalline–isotropic phase transition appeared in the DSC thermograms, whereas the biphenol‐based homopolymer had only a melting transition. The novel poly(aryl ether ketones) had glass‐transition temperatures that ranged from 143 to 151°C and lower Tm's that ranged from 279 to 291°C, due to the copolymerization. The polymers showed high thermal stability, and some exhibited a large range in mesophase stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1347–1350, 2003 相似文献
16.
Poly(butylene 2,6‐naphthalate) (PBN)/poly(ethylene glycol) (PEG) copolymers were synthesized by the two‐step melt copolymerization process of dimethyl‐2,6‐naphthalenedicarboxylate (2,6‐NDC) with 1,4‐butanediol (BD) and PEG. The copolymers produced had different PEG molecular weights and contents. The structures, thermal properties, and hydrophilicities of these copolymers were studied by 1H NMR, DSC, TGA, and by contact angle and moisture content measurements. In particular, the intrinsic viscosities of PBN/PEG copolymers increased with increasing PEG molecular weights, but the melting temperatures (Tm), the cold crystallization temperatures (Tcc), and the heat of fusion (ΔHf) values of PBN/PEG copolymers decreased on increasing PEG contents or molecular weights. The thermal stabilities of the copolymers were unaffected by PEG content or molecular weight. Hydrophilicities as determined by contact angle and moisture content measurements were found to be significantly increased on increasing PEG contents and molecular weights. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2677–2683, 2006 相似文献
17.
Previous studies have evaluated low molecular weight crystalline materials as latent heat sinks for passive thermal protection systems. This study evaluated crystalline polymers as heat storage materials. Differential scanning calorimetry and Instron thermomechanical analysis are applied in dynamic studies of cumulative histories of melting and recrystallization. Commercially available crystalline polymers with melting temperatures Tm ≥ 100°C can provide fully reversible heats of fusion ΔHm ≥ 35 cal/gm under programmed heating-cooling cycles. A linear polyethylene (Marlex 6050) is modified by radiation crosslinking to retain shape stability above Tm with-out loss of heat storage capability. The essentially zero vapor pressure and inherent shape stability of crosslinked crystalline polymers may provide unique advantages as uncontained, non-expendable, heat storage materials. 相似文献
18.
W. Maung K. M. Chua T. H. Ng H. Leverne Williams 《Polymer Engineering and Science》1983,23(8):439-445
Representative random, alternating block copolymers of polydimethylsiloxane (PDMS) and bisphenol-A-polycarbonate (BPAPC) were studied by thermomechanical and dynamic mechanical techniques. Data on glass transition temperatures (Tg), heat-deflection temperatures (Td), Vicat softening temperatures (Ts), coefficients of linear expansion (α), stress-strain, and stress relaxation for four PDMS-BPAPC block co-polymers are presented. The effect of casting films from mixed n-hexane-methylene chloride solution on the thermomechanical and dynamic mechanical properties was also studied. 相似文献
19.
Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/phenolic blends are new miscible crystalline/amorphous polymer blends prepared via solution casting method in this work, as evidenced by the single composition dependent glass transition temperature. The measured Tgs can be well fitted by the Kwei equation with a q value of 13.6 for the PHBV/phenolic blends, indicating that the interaction between the two components is strong. The negative polymer–polymer interaction parameter, obtained from the melting depression of PHBV using the Nishi‐Wang equation, indicating the thermal miscibility of PHBV and phenolic. The spherulitic morphology and crystal structure of PHBV/phenolic blends were studied with polar optical microscopy and wide angle X‐ray diffraction compared with those of neat PHBV. It is found that the growth rates of PHBV in the blends are lower than that in neat PHBV at a given crystallization temperature, and the crystal structure of PHBV is not modified by the presence of phenolic in the PHBV/phenolic blends, but the crystallinity decrease with the increasing of phenolic. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
20.
K. E. Hardenstine C. J. Murphy R. B. Jones L. H. Sperling G. E. Manser 《应用聚合物科学杂志》1985,30(5):2051-2064
Diblock, triblock, and alternating block copolymers based on poly[3,3-bis(ethoxymethyl) oxetane] [poly(BEMO)] and a random copolymer center block poly(BMMO-co-THF) composed of poly[3,3-bis(methoxymethyl)oxetane] [poly(BMMO)], and poly(tetrahydrofuran) [poly(THF)] were synthesized and characterized with respect to molecular weight. Glass transition temperatures Tg and melting temperatures Tm were characterized via DSC, modulus–temperature, and dynamic mechanical spectroscopy (DMS). These polyethers had Tm between 70°C and 90°C, and Tg between ?55°C and ?30°C. The degree of crystallinity of poly(BEMO) was found to be 65% by X-ray powder diffraction. Tensile properties of the triblock copolymer, poly(BEMO-block-BMMO-co-THF-block-BEMO) were also studied. A yield point was found at 4.1 × 107 dyn/cm2 and 10% elongation and failure at 3.8 × 107 dyn/cm2 and 760 % elongation. Morphological features were examined by reflected light microscopy and the kinetics of crystallization were studied. Poly(BEMO) and its block copolymers were found to form spherulites of 2–10 μm in diameter. Crystallization was complete after 2–5 min. 相似文献