Synthesis and characterization of poly(dimethyl siloxane) containing poly(vinyl pyrrolidinone) block copolymers

ABA‐type block copolymers containing segments of poly(dimethyl siloxane) and poly(vinyl pyrrolidinone) were synthesized. Dihydroxyl‐terminated poly(dimethyl siloxane) was reacted with isophorone diisocyanate and then with t‐butyl hydroperoxide to obtain macroinitiators having siloxane units. The peroxidic diradical macroinitiators were used to polymerize vinyl pyrrolidinone monomer to synthesize ABA‐type block copolymers. By use of physicochemical methods, the structure was confirmed, and its characterization was accomplished. Mechanical and thermal characterizations of copolymers were made by stress–strain tests and differential scanning calorimetric measurements. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1915–1922, 1999     

Formation of bubbles during ultrasonic treatment of cured poly(dimethyl siloxane)

A static ultrasonic treatment device was used to investigate the effect of ultrasound on degradation of unfilled poly(dimethyl siloxane) (PDMS) vulcanizate in the absence of shearing effect. The effects of pressure, ultrasound intensity and thickness of the disks upon ultrasonic treatment were investigated. The power consumption was measured as a function of sample thickness, ultrasonic amplitude, and applied pressure. The dynamics of bubble (nucleation, growth and coalescence) was also studied with respect to applied pressure and amplitude. An increase in thickness of the sample was observed during ultrasonic treatment. The unique correlation between gel fraction and crosslink density obtained in the present static experiments was compared with those of continuous devulcanization studied earlier.     

Studies of cyclic and linear poly(dimethyl siloxanes):7. Diffusion behaviour in a poor solvent

The diffusion coefficients (D) of cyclic and linear poly(dimethylsiloxanes) (PDMS) have been measured in bromocyclohexane at 288 K and 301 K. Bromocyclohexane has previously been reported to be a θ-solvent for high molar mass linear PDMS at 301 K, but the hydrodynamic radii reported here apparently show the effects of molecular expansion at both temperatures. In addition, the hydrodynamic radii of both linear and cyclic PDMS are found to be insensitive to whether the solvent is toluene or bromocyclohexane. The ratio of friction coefficients $\text{f}{}_{\mathrm{r}}\text{f}{}_{\mathrm{l}}$ for the ring (r) and linear (l) molecules of the same number of segments (x) is in good agreement with the theoretical value of $\text{8}\text{3π}$ in the impermeable limit and with the experimental value found previously in toluene solution. As x decreases the ratio $\text{f}{}_{\mathrm{r}}\text{f}{}_{\mathrm{l}}$ tends to unity, illustrating the increasing importance of free-draining at low molar mass.     

Electrospinning of poly(dimethyl siloxane) by sol–gel method

Crosslinked poly(dimethyl siloxane) (PDMS) fibers were fabricated by electrospinning in combination with a sol–gel process followed by heat treatment. Before and after heat treatment, the changes in the chemical and thermal properties of the electrospun PDMS fibers were examined by differential scanning calorimetry (DSC), equilibrium swelling tests, and contact angle measurements. There was no significant change in morphology and average diameter of the as‐spun PDMS fibers after heat treatment. The tensile properties of the as‐spun PDMS fibers mat increased with increasing heat treatment temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Development of wear-resistant thermoplastic polyurethanes by blending with poly(dimethyl siloxane). II. A packing model

It has been shown in a previous article that melt blending of low levels of commercial poly(dimethyl siloxane) (PDMS) fluid with commercial thermoplastic polyurethanes has a significant positive impact on the coefficient of friction (CoF) and on the mechanical and wear properties of the polyurethanes. The improvements in CoF and wear resistance were expected due to surface modification of the polymer; however, the improvements in the mechanical properties were much more significant than expected. Evidence presented in the earlier publication suggests that the changes in the wear and mechanical properties are not due to surface modification alone, but are largely due to modification of the bulk by PDMS. In this article a model is presented that accounts for the observed relationship between PDMS content and the properties of the blends. It is proposed that the addition of PDMS facilitates an improved packing efficiency (antiplasticization) in the polyurethane soft domain, leading to improved material performance. Beyond an optimum PDMS concentration of 1.5–2.0%, phase separation of PDMS becomes significant, plasticization sets in, and mechanical properties then begin to diminish rapidly. This model has been rigorously investigated and has proven to be highly robust. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:939–950, 1997     

Synthesis and physical properties of poly(l‐lactic acid)‐poly(dimethyl siloxane) multiblock copolymers prepared by direct polycondensation

Multiblock copolymers consisting of poly(l ‐lactic acid) and poly(dimethyl siloxane) were prepared by the polycondensation of oligo(l ‐lactic acid) (OLLA) with dihydroxyl‐terminated oligo(dimethyl siloxane) and dicarboxyl‐terminated oligo(dimethyl siloxane). Copolymers with number‐average molecular weights of 18,000?33,000 Da and various content ratios of oligo(dimethyl siloxane) (ODMS) unit were obtained by changing the feed ratio of these oligomers. A film prepared from the copolymer with an ODMS content ratio of 0.37 exhibited two independent peaks at ?107°C and 37°C in the mechanical loss tangent for temperature dependence, suggesting the formation of microphase separation between the OLLA and ODMS segments. The film had a tensile strength of 3.2 MPa and a high elongation of 132%. The film also exhibited a high strain recovery even after repeated straining. The incorporation of dimethyl siloxane units as multiblock segments was confirmed to improve the flexibility of poly(l ‐lactic acid). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40211.     

Studies of cyclic and linear poly(dimethyl siloxanes): 8. Light scattering measurements in good and poor solvents

Weight average molar masses (M_w) and second virial coefficients (A₂) have been measured for linear and cyclic poly(dimethyl siloxane) (PDMS) fractions in toluene at 298K and for linear PDMS in bromocyclohexane at 301K. The values of M_w are compared with those deduced previously using gel permeation chromatography, broadly confirming the values already assigned to the fractions. The values of A₂ for linear PDMS in toluene are shown to be consistent with previously published values for oligomeric linear PDMS. The values of A₂ for cyclic PDMS approach those of linear PDMS for M_w<～1000 g mol^?1 and decrease more rapidly as M_w increases in approximate agreement with theoretical predictions. In addition, the conventional relations between A₂ and the expansion factor α_s are shown to be inapplicable at low molar mass.     

聚亚苯基硅氧烷交联网络的热性能

用Si—H/Si—OR缩聚的方法制备了含可交联乙烯基的聚亚苯基硅氧烷-二甲基硅氧烷共聚物(PTMPS-DMS),用硅氢加成、BPO热交联两种方法进行交联得到交联网络,并用热重分析(TG)、300℃恒温热分析和DSC等方法对其热性能进行了研究。结果表明,交联方法对PTMPS-DMS交联网络的热稳定性影响很大,BPO热交联网络的热稳定性远远高于硅氢加成交联网络,两种交联网络在空气中的5%热失重温度分别是480℃和368℃,Tg则没有显著差异,分别是-55℃和-49℃。H2PtCl6能显著降低PTMPS-DMS及其交联网络在空气中的热稳定性。     

Studies of cyclic and linear poly(dimethyl siloxanes): 9. Quasi-elastic light scattering and concentration dependences of diffusion coefficients

The concentration dependences of the diffusion coefficients (D) of linear and cyclic poly(dimethyl siloxanes) (PDMS) in toluene at 298K are reported. Three cyclic/linear pairs of fractions with molar masses in the range 300 to 23 500 g mol^?1 were used. The values of D obtained by quasielastic scattering were in good agreement with those measured by the classical boundary-spreading technique. Analysis of the concentration dependences in terms of the theory of Pyun and Fixman indicates that the solute molecules show a minimum of interpenetration in toluene at 298K.     

Synthesis and characterization of poly(ester ether siloxane)s

A series of novel thermoplastic elastomers based on ABA‐type triblock prepolymers, poly[(propylene oxide)–(dimethylsiloxane)–(propylene oxide)] (PPO‐PDMS‐PPO), as the soft segments, and poly(butylene terephthalate) (PBT), as the hard segments, was synthesized by catalyzed two‐step melt transesterification of dimethyl terephthalate (DMT) with 1,4‐butanediol (BD) and α,ω‐dihydroxy‐(PPO‐PDMS‐PPO) (M?_n = 2930 g mol^?1). Several copolymers with a content of hard PBT segments between 40 and 60 mass% and a constant length of the soft PPO‐PDMS‐PPO segments were prepared. The siloxane‐containing triblock prepolymer with hydrophilic terminal PPO blocks was used to improve the compatibility between the polar comonomers, i.e. DMT and BD, and the non‐polar PDMS segments. The structure and composition of the copolymers were examined using ¹H NMR spectroscopy, while the effectiveness of the incorporation of α,ω‐dihydroxy‐(PPO‐PDMS‐PPO) prepolymer into the copolyester chains was controlled by chloroform extraction. The effect of the structure and composition of the copolymers on the transition temperatures (T_m and T_g) and the thermal and thermo‐oxidative degradation stability, as well as on the degree of crystallinity, and some rheological properties, were studied. Copyright © 2006 Society of Chemical Industry     

Studies of cyclic and linear poly(dimethyl siloxanes): 14. Particle scattering functions

Particle scattering functions P(Q) (where Q represents the wave vector), have been calculated using a Monte Carlo method for cyclic and linear poly(dimethyl siloxanes) (PDMS) containing up to 100 skeletal bonds. A maximum is found in the Kratky plot at $\text{u (=Q〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)≈2.0}$ for cyclic PDMS (with root-mean-square radii of gyration $\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) and this is in satisfactory agreement with the analytical calculations of Casassa and of Burchard and Schmidt. In addition, other clearly-defined maxima are found at u≈5.0 for PDMS ring molecules with less than ≈40 skeletal atoms. These maxima are believed to be characteristic of small cyclic molecules as they are also predicted for small polymethylene rings. Comparisons are made with experimental small-angle neutron scattering (SANS) data for cyclic and linear PDMS. A single maximum in the experimental Kratky plot at u≈2.0 is found for PDMS ring molecules with an average of 550 skeletal atoms. The experimental data for cyclic PDMS are in better agreement with the Monte Carlo calculations of P(u) than with analytical predictions up to u≈2.0.     

The influence of loose and semianchored siloxane polymer chains on the tack of crosslinked silicone rubber

The influence of addition of nonreactive silicone oil or semianchored silicone polymer on crosslinked poly(dimethylsiloxane) (PDMS) rubber–rubber adhesion was studied. The additives can be considered either a tackifier, or connector molecules, able to cross the interface and entangle. In both cases, it influences the tack of the elastomers. An additional variable is the molecular weight of the additive, which affects the reptation of the polymer chains. Polymer–polymer demixing, which is the result of thermodynamic incompatibility of mixed polymers is another factor that influences tack. It causes the free chains to appear at the surface forming a layer of oil, which actually destroys the tack of the PDMS samples. The resulting tack phenomena as a function of oil, respectively semianchored silicone polymer chains, are very much dependent on the transient nature of the polymer reptation: in many cases the polymers need very long time periods to obtain equilibrium in interphase crossing, or oil sweats out of the crosslinked polymers, forming a liquid layer between the two phases resulting in a low tack value, due to hydrodynamic wetting alone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and flame resistance properties of natural rubber‐g‐poly‐(dimethyl(methacryloyloxymethyl)phosphonate)

Natural rubber grafted with poly(dimethyl(methacryloyloxymethyl)phosphonate) (i.e., NR‐g‐PDMMMP) was prepared in latex medium via photopolymerization. Thermal and flame resistance properties of the NR‐g‐PDMMMP prepared with various levels of grafted PDMMMP or grafting rate (GR) were investigated. Thermal behaviors were investigated by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). It was found that the graft copolymer exhibited phase separation with double T_g values. A shift of T_gs toward each other was observed with increasing GR, which indicated tendency to become a single phase material. Increasing GRs also caused increasing heat and flame resistance with increasing degradation temperature and level of char residue. Furthermore, increasing level of limited oxygen index (LOI) and decreasing burning rate were observed with increasing the GR. This is attributed to increasing content of char residue of the phosphorus compound, which acted as the thermal insulation and a barrier of oxygen to transfer to the burning materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Determination of exchange enthalpy and entropy parameters of poly(dimethyl siloxane) with some n-alkanes by inverse gas chromatography

The total interaction parameter at infinitely high polymer concentration. χ_t^∞, and the effective exchange energy parameter, X̄₁₂, of poly(dimethyl siloxane) with n-pentane, n-hexane, n-heptane and n-nonane were determined around room temperature using the inverse gas chromatography technique. The values of χ_t^∞ are in agreement with corresponding literature values. The exchange enthalpy X₁₂ and entropy, Q₁₂, parameters were determined at the same temperature. The X₁₂ parameters increase with the carbon number of the n-alkanes, while their temperature dependence is almost negligible. The Q₁₂ parameters are approximately independent of temperature and carbon number of the n-alkanes.     

Toughness enhancement of poly(lactic acid) by melt blending with natural rubber

Rubber toughened poly(lactic acid) (PLA) was prepared by blending with natural rubber (NR)‐based polymers. The blends contained 10 wt % of rubber and melt blended with a twin screw extruder. Enhancement of impact strength of PLA was primarily concernced. This study was focused on the effect of rubber polarity, rubber viscosity and molecular weight on mechanical properties of the blends. Three types of rubbers were used: NR, epoxidized natural rubber (ENR25 and ENR50), and natural rubber grafted with poly(methyl methacrylate) (NR‐g‐PMMA). Effect of viscosity and molecular weight of NR, rubber mastication with a two‐roll mill was investigated. It was found that all blends showed higher impact strength than PLA and NR became the best toughening agent. Viscosity and molecular weight of NR decreased with increasing number of mastication. Impact strength of PLA/NR blends increased after applying NR mastication due to appropriate particle size. DMTA and DSC characterization were determined as well. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Studies of cyclic and linear poly(dimethyl siloxanes): 13. Static dielectric measurements and dipole moments

The static dielectric permittivities, refractive indices and densities of undiluted oligomeric cyclic and linear dimethyl siloxanes and narrow fractions of cyclic and linear poly(dimethyl siloxanes) have been measured for number-average molar masses M?_n in the range $\text{160 <}\text{M}\text{?}{}_{\mathrm{n}}\text{< 7700}$ at temperatures from 298 to 313 K. Measured total dielectric polarizations have been resolved into their electronic, atomic and orientation components and dipole moments have been derived. The dipole moments of cyclic oligomers ((CH₃)₂SiO)_x (for example, with x = 4, 5) are markedly lower than the dipole moments of the corresponding linear oligomers containing the same number of siloxane bonds. However, for x ? 10, the dipole moments of cyclic dimethyl siloxanes are identical, within experimental error, to those of the corresponding linear dimethyl siloxanes. Measured static dielectric permittivities of the dimethyl siloxanes and poly(dimethyl siloxanes) in solution in cyclohexane are markedly different from the corresponding values for the undiluted siloxanes. These differences are interpreted as resulting from the specific solvent effects.     

Grafting of poly(vinyl alcohol) on natural rubber latex particles

Poly(vinyl alcohol) (PVA) was grafted on natural rubber (NR) latex particles (NR‐g‐PVA) using potassium persulfate to generate active radicals on both NR particle surface as well as PVA molecules. ¹H‐ and ¹³C‐nuclear magnetic resonance spectroscopy suggested a possibly chemical attachment of PVA on the NR. The amount of graft‐PVA expressed in term of grafting percentage (%G) increased almost linearly with the amount of PVA adding to the NR latex. Measuring by dynamic light scattering, the particle size of NR‐g‐PVA particles was larger than the size of unmodified NR, also it increased with the molecular weight and %G of PVA. Transmission electron microscopy images of the NR‐g‐PVA latex particles revealed that the size of PVA‐grafted NR particle was enlarged by a layer of graft‐PVA surrounding the NR particle. Given by the graft‐PVA layer surrounding NR particles, the NR‐g‐PVA latex particles possessed better colloidal stability as lowering pH compared with the unmodified NR latex. Comparing with unmodified NR particles, the electrophoretic mobility of NR‐g‐PVA particles was lower due to the presence of graft‐PVA that shifted the shear plane further away from the surface of the particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Studies of cyclic and linear poly(dimethyl siloxanes): 10. Calculations of radii of gyration

A Monte Carlo method has been devised for calculating the conformation-dependent properties of cyclic poly(dimethyl siloxanes) (PDMS), using Flory, Crescenzi and Mark's rotational isomeric state model. Calculated values of the mean-square radii of gyration 〈s²_r〉 of ring molecules unperturbed by excluded volume effects and containing 8–100 skeletal atoms are compared with the 〈s²_l〉 values for the corresponding unperturbed chain molecules. Exact enumeration methods were also employed for rings $\text{[(}\text{CH}{}_3\text{)}{}_2\text{SiO}\text{]}{}_{\mathrm{<mtext>w</mtext><mtext>2</mtext>}}$ with w ? 24 and the results found to be in close agreement with those obtained by the Monte Carlo method. The ratio $\text{〈s}{}^2{}_{\mathrm{l}}\text{〉}\text{〈s}{}^2{}_{\mathrm{r}}\text{〉}$ was found to attain limiting values close to 2.0 for w > 30, in agreement with theoretical predictions.     

Fabrication and characterization of TiO2/poly(dimethyl siloxane) composite fibers with thermal and mechanical stability

The mechanical stability of titania (TiO₂) nanofibers was improved by fabricating TiO₂/poly(dimethyl siloxane) (PDMS) composite fibers using a combination of hybrid electrospinning and sol‐gel methods, followed by heat treatment at 250°C for 3 h. The compositions (90/10, 80/20, and 70/30, w/w) of the TiO₂/PDMS composite fibers were varied by adjusting the flow rate of the PDMS sol with the flow rate of TiO₂ sol fixed. There was no significant change in morphology and average diameter of the as‐spun TiO₂/PDMS fibers after heat treatment. Both the tensile strength and modulus of the TiO₂/PDMS composite fibers increased gradually with increasing PDMS content up to 30 wt %. In addition, from the photo‐degradation reaction of methylene blue, the photocatalytic activity of TiO₂/PDMS composite fibers was strongly dependent on the TiO₂ content (%) in the composite fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Compatibilization of poly(lactic acid)/epoxidized natural rubber blend with maleic anhydride

The objective of this work was to determine the compatibilization effect of different concentrations of maleic anhydride (MA) in poly(lactic acid) blended with epoxidized natural rubber (PLA/ENR). ENR-grafted MA [ENR-g-MA] was synthesized using four concentrations of MA: 0.15, 0.30, 0.45, and 0.60 phr. Using an internal mixer, binary (PLA/ENR, PLA/ENR-g-MA) and ternary (PLA/ENR/ENR-g-MA) polymer blends were prepared with a constant rubber content of 10 wt %. ENR impaired the mechanical properties of PLA, perhaps due to the relatively large size of the rubber particles. The compatibilization effect of MA was evaluated from the results of impact strength testing. ENR-g-MA was a toughening agent for PLA when the concentration of MA was in the range of 0.30–0.60 phr. MA increased miscibility between PLA and ENR. This effect was indicated in the blends by reductions in rubber particle size, the glass transition temperature of PLA, and the α-transition temperatures of PLA and ENR. In the binary polymer blends, the MA concentration in ENR-g-MA that produced the optimal mechanical properties of PLA was 0.60 phr. In the ternary blends, mechanical properties of PLA did not improve at any concentration of MA in ENR-g-MA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48297.