Randomly branched styrene/divinylbenzene copolymers. I. Preparation,molecular weight characterization,and GPC analysis

A series of randomly branched copolymers of styrene and divinylbenzene were prepared using a benzoyl peroxide-initiated free-radical bulk polymerization at 78°C. DVB contents were varied from 0.01% to 2%. Two samples were polymerized with 0.4% DVB to different conversions: series 9A at 6% conversion and series 9B at 15% conversion (just short of the gelation point). Both samples were fractionated and the fractions characterized by ultracentrifugation, light scattering, osmometry, viscometry, and gel permeation chromatography. The data indicated that the fractions were not of narrow MWD and that the breadth of the MWD of the fractions from series 9B were greater than those of 9A. GPC calibration curves of M, [η], and M [η] were generated for both 9A and 9B fractions by employing curve-fitting techniques to the GPC data. For all of the fractions 9B, the molecular weight calibration provided accurate values of M?_z, M?_w, and M?_n, suggesting that no serious peak spreading had occurred in the GPC experiments. The universal calibration parameter M[η] for the 9A fractions agreed with that of linear polystyrene, while that of the high-conversion series 9B did not. It will be shown in a later paper that series 9B is highly branched, while 9A is lightly branched. Consequently, it is recommended that any GPC analysis of branching units make an allowance for the deviation of highly branched polymers from the linear M[η] calibration curve.     

Characterization of Anadenanthera macrocarpa exudate polysaccharide

Exudate gum from Anadenanthera macrocarpa Benth. trees was purified and fractionated using 0·1M aq. NaCl/ethanol as a solvent/non-solvent system. The composition of the polysaccharide was determined as 67% arabinose, 24% galactose, 2% rhamnose and 7% glucuronic acid, by a combination of high performance liquid chromatography of fully hydrolysed gum and colorimetric analysis of uronic acid. Molecular characteristics of the polysaccharide and its fractions were investigated by light scattering intensity, dilute solution visco-metry and gel permeation chromatography (GPC). The whole gum was shown to possess a broad molar mass distribution with Mw = 3·7×10⁶ g mol^-1 and [η] = 11cm³ g^-1. Hydrodynamic properties indicated a highly branched structure. Fractions were obtained covering a range of molar masses. The intrinsic viscosity in 1·0 M aq. NaCl at 25°C was found to depend on molar mass according to: [η]/cm³ g^-1 =0 ·0145 M^0·44. The hydrodynamic volume parameter [η]M gave a common GPC calibration for branched polysaccharide fractions and linear poly(oxyethylene) standards. ©1997 SCI     

Evaluation of different branching functions used in the determination of random branching by GPC

Three branching functions are evaluated for use in the measurement of random branching by GPC. Initial evaluations of the functions g^1/2, g^3/2, and h³ were made by computer simulations of GPC experiments using published data of lightly and highly randomly branched polymers. Actual GPC experiments were then performed on characterized samples of lightly and highly branched styrene–divinylbenzene copolymers. The results indicate that h³ adequately predicts branching and molecular weight at all branching densities, whileg^1/2 is accurate only for lightly branched polymers and g^3/2 is accurate only for highly branched polymers. A means for predicting the M–[η] curve for branched polymers from the M–[η] calibration curve for linear polymer is proposed.     

Dilute solution properties of randomly branched poly(methyl methacrylate)

Randomly branched poly(methyl methacrylate) samples were prepared by copolymerization with different amounts of ethylene dimethacrylate. The molecular weight distributions, radius of gyration distributions, and intrinsic viscosity distributions were measured by size exclusion chromatography with refractive index, multiangle light-scattering, and viscosity detectors. The effect of branching on the radius of gyration was compared with the effect on the intrinsic viscosity. It was found that the intrinsic viscosity contraction factor gⁱ scales with the radius of gyration contraction factor g, with the exponent, ϵ, having a value in the range 0.8–1.0. © 1996 John Wiley & Sons, Inc.     

Preparation of heat‐resistant branched poly(styrene‐alt‐NPMI) by ATRP with divinylbenzene as the branching agent

Heat‐resistant branched poly(styrene‐alt‐NPMI) has been prepared via atom transfer radical polymerization (ATRP) of styrene (St) and N‐phenyl maleimide (NPMI) with divinylbenzene (DVB) as the branching agent in anisole at 80°C. Gas chromatography (GC) was used to determine the conversion of the reactants. Triple detection gel permeation chromatography (TD‐GPC) was used to analyze the copolymers. The results show that the polymerization yields primary chains predominately in the early stages and the formation of branched molecules occurs mainly when conversion is higher than 50%. As expected, higher dosage of DVB in our investigation range favors the formation of polymers with higher degree of branching. All the resulting branched poly(styrene‐alt‐NPMI)s have glass transition temperature (T_g) above 175°C, extrapolated initial weight loss temperature (T_i) above 410°C and statistic heat‐resistant index above 200°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Segregation of resin‐bound peptides during solid‐phase synthesis

To compare the segregation ability of 1,4‐butanediol dimethacrylate‐crosslinked polystyrene (BDDMA‐PS) and divinylbenzene‐crosslinked polystyrene (DVB‐PS), a set of difficult sequence peptides characterized by high‐arithmetic‐average β‐sheet stabilizing potential (SP_β) and low‐stepwise arithmetic average random coil conformational parameter (P_c*) were synthesized on both supports (～ 2 mmol Cl g^?1) under identical conditions. The yield and purity of the peptides obtained from BDDMS‐PS resin were higher than from DVB‐PS resin. The synthetic efficiency of the new support was found to be its ability to suppress the aggregation of growing peptide chains by β‐sheet formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1717–1723, 2002     

Mark–Houwink equation and GPC calibration for linear short-chain branched polyolefines,including polypropylene and ethylene–propylene copolymers

The reduction in molecular dimensions due to the presence of short side chains in otherwise linear polyolefins can very simply by calculated by assuming that the configuration of the main chain is not influenced by the side chains. This enables us to express the intrinsic viscosity–molar mass relationship as a function of the mass fraction of side chains (S): [η] = (1 ? S)^α+1K_PEM_ν^α and, with use of the universal calibration principle, to convert the GPC calibration for purely linear polymers samples into the calibration for short-chain branched polymers: M^* = (1 ? S)M. Experimental data from literature on short-chain branched poly-ethylenes, and our own data on ethylene–propylene copolymers are used to verify the above assumption. It appears that the experimentally found relations between [η], M_w and M^*_w (GPC) within the usual accuracy justify this approach.     

Dependence of intrinsic viscosity and molecular size on molecular weight of partially hydrolyzed polyacrylamide

As a typical water-soluble polymer, ultra-high molecular weight (UHMW) partially hydrolyzed polyacrylamide (HPAM) has been widely used in various industries as thickeners or rheology modifiers. However, precise determination of its critical physical parameters such as molecular weight, radius of gyration (R_g) and hydrodynamic radius (R_h) were less documented due to their high viscosity in aqueous solution. In this work, the molecular structure of five UHMW-HPAM samples with different MW was elucidated by ¹H and ¹³C NMR spectroscopy, and their solution properties were characterized by both static and dynamic light scattering. It is found that all the second virial coefficient (A₂) values are positive and approaching zero, indicating of a good solvent of 0.5 M NaCl for UHMW-HPAM. The weight-average molecular weight (M_w) dependence of molecular size and intrinsic viscosity [η] for these series of HPAM polymers with MW ranging from 4.81 to 15.4 × 10⁶ g·mol⁻¹ can be correlated as R_g = 3.52 × 10⁻²M_w^0.51, R_h = 1.97 × 10⁻²M_w^0.51, and [η] = 6.98 × 10⁻⁴ M_w^0.91, respectively. These results are helpful in understanding the relationship between molecular weight and coil size of HPAM polymers in solution, and offer references for quick estimation of molecular weight and screening of commercial UHMW-HPAM polymers for specific end-users.     

Molecular weight and chain conformation of amylopectin from rice starch

By using laser light scattering (LS) and size exclusion chromatography combined LS, we have investigated the molecular weight and chain conformation of amylopectin from rice of India (II‐b), japonica (IJ‐b), and glutinous (IG‐b) in dimethyl sulfoxide (DMSO) solution. The weight‐average molecular weight (M_w) and radius of gyration (〈S²〉^½) of amylopectin were determined to be 4.06 × 10⁷ and 128.5 nm for India rice, 7.41 × 10⁷ and 169.6 nm for japonica rice, 2.72 × 10⁸ and 252.3 nm for glutinous rice, respectively. The 〈S²〉^½ values were much lower than that of normal polymers, indicating a small molecular volume of amylopectin, as a result of highly branched structure. Ignoring the difference of degree of branching, approximated dependences of 〈S²〉^½ and intrinsic viscosity ([η]) on M_w for amylopectin in DMSO at 25°C were estimated to be 〈S²〉^½ = 0.30M_w^0.35 (nm) and [η] = 0.331M_w^0.41 (mL g^?1) in the M_w range studied. Moreover, from the 〈S²〉^½ values of numberless fractions obtained from many experimental points in the SEC chromatogram detected with LS, the dependence of 〈S²〉^½ on M_w for the II‐b sample was estimated also to be 〈S²〉^½ = 0.34 M_w^0.347, coinciding with the above results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of crosslinked polystyrene-grafted PFA films by a simultaneous irradiation method

A series of polystyrene (PS)/divinylbenzene (DVB)-grafted poly(tetrafluoroethylene-co-perfluorovinyl vinyl ether) (PFA) films with various DVB contents were prepared by a simultaneous radiation grafting method. The degree of grafting was found to be strongly dependent on the grafting conditions, such as the monomer concentration, irradiation dose, dose rate, and crosslinker concentration. The results show that the highest degree of grafting was achieved at a 10% DVB content at the same irradiation conditions. The prepared PFA-g-PS/DVB films were characterized using FTIR, TGA, and a mechanical strength test.     

Synthesis and Polymerization of Epoxy Methacrylates, 2. Acylated Epoxy Methacrylates and their Copolymers

Partially (20–75%) acylated isopropylidene‐bis[1,4‐phenyleneoxy(2‐hydroxytrimethylene)] dimethacrylate (BisGMA) was prepared by a single step reaction of 2,2‐bis[4‐(2,3‐epoxypropoxy)phenyl]propane (DGEBA) with methacrylic acid (MAA), methacrylic anhydride (MAAn) and/or acetic anhydride catalyzed by 0.8 mol‐% N‐methylimidazole at 90–100°C. In any case, MAA was substituted by an equimolar quantity of the anhydride. The reaction kinetics of DGEBA with MAA and MAAn follows a first order law up to a conversion of epoxy groups corresponding to the initial molar ratio of MAAn. For different mole fractions x_MAA, the reaction rate was found to be directly proportional to x^0.5_MAA. The viscosity of BisGMA decreased with an increase in the acylation degree. Acylated BisGMA was copolymerized with triethylene glycol dimethacrylate (TEGMA) by use of a redox initiator system at room temperature and with vinyltoluene (VT) initiated by di‐tert‐butyl peroxide at 150–200°C, respectively, both in the presence of 70–76 wt.‐% of quartz filler. Different dependencies of the content of sol and the conversion of C=C double bonds were observed for thermally polymerized composites from VT with acetylated and methacrylated BisGMA, respectively. Methacrylated BisGMA yielded composites with reduced water uptake. The higher network density of the polymer matrix with methacrylated BisGMA resulted in a higher glass transition temperature T_g and a higher storage modulus of the composites. The initial temperature of weight loss of composites with VT was increased from 230°C for composites with BisGMA up to 258°C for composites with BisGMA methacrylated to a degree of 40%.     

Molecular architectures of four‐arm star‐shaped styrene‐butadiene copolymer

To understand the molecular architectures of styrene‐butadiene four‐arm star (SBS) copolymers, a size exclusion chromatography combined with laser light scattering (SEC‐LLS) has been used to determine their weight‐average molecular weight (M_w) and radius of gyration (〈S²〉^1/2), and a new method for the establishment of the Mark‐Houwink equation from one sample has been developed. Based on the Flory viscosity theory, we successfully have reduced the 〈S²〉^1/2 values of numberless fractions estimated from many experimental points in the SEC chromatogram to intrinsic viscosities ([η]). For the first time, the dependences of 〈S²〉^1/2 and [η] on M_w for the four‐arm star SBS in tetrahydrofuran at 25°C were found, respectively, to be 〈S²〉^1/2 = 2.62 × 10^?2 M (nm) and [η] = 3.68 × 10^?2 M (mL/g) in the M_w range from 1.4 × 10⁵ to 3.0 × 10⁵. From data of [η] and 〈S²〉^1/2 for linear and star SBS, we have obtained the information about the branching, namely, the ratios (g and g′) of 〈S²〉 and [η] for star SBS to that of the linear SBS of the same molecular weight, which agree with theoretical predictions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 961–965, 2005     

Crystallisation kinetics of novel branched poly(ethylene terephthalate): a small‐angle X‐ray scattering study

Three types of poly(ethylene terephthalate) (PET) were investigated: linear (unprocessed) bottle‐grade PET (intrinsic viscosity, IV ～ 0.82 dL g^?1); a branched PET produced from linear PET by reactive extrusion with 0.4% w/w pyromellitic dianhydride and pentaerythritol in 5:1 molar ratio (IV ～ 0.97 dL g^?1); and a control sample produced from the same linear PET by extrusion under the same conditions without the reactive agents (IV ～ 0.71 dL g^?1). A key finding is that the reactive extrusion process, presumably as a consequence of branching and branch distribution, significantly modifies the crystallisation kinetics and changes the final morphology. Using small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC), the crystallisation kinetics of PET was monitored from the melt (270 °C) to a crystallisation temperature of either 205 or 210 °C. The IV of the branched PET was ～ 21% greater than that of the unprocessed PET, and the rate of melt crystallisation (from DSC measurements) was 510 s for the branched, 528 s for the control, and 640 s for the unprocessed PET. The lamellae spacings measured from the equilibrium SAXS patterns were ～160 ± 10 Å for the branched PET and ～180 ± 10 Å for the unprocessed PET. Such properties offer the potential for new applications requiring high‐melt‐strength PET. Copyright © 2006 Society of Chemical Industry     

Studies on the development of branching in ATRP of styrene and acrylonitrile in the presence of divinylbenzene

Branching atom transfer radical polymerization (ATRP) of styrene and acrylonitrile was attempted in the presence of divinylbenzene targeting toward soluble branched copolymer. The kinetics and the development of branching with monomer conversion were studied in detail. Gas chromatography (GC), gel permeation chromatography (GPC) coupled with multi-angle laser light scattering (MALLS), proton nuclear magnetic resonance (¹H NMR) spectroscopy and intrinsic viscosity determination were used to monitor the polymerization process and characterize the obtained copolymer. Analysis of conversion of reactants, the growth manner of molecular weight with monomer conversion and GPC traces proved that the primary chains with low polydispersity formed mainly at the early stage and then were linked in a statistical manner to start the branching at the middle or late stage. The more the branching agent was used, the earlier the branching occurred, and too much higher level of branching agent resulted in gelation. For the selected ratio of [t-BBiB]/[DVB]/[St]/[AN] = 1/0.9/15/15, with monomer conversion less than 40%, primary chains with low polydispersity formed from the polymerization of St, AN and DVB, and only a part of the primary chains contained pendent vinyl group. When monomer conversion was up to 40%, the pendent vinyl groups participated in polymerization, resulting in the linking of the primary chains statistically to start the branching. The branching became significant at monomer conversion up to 50%, giving rise to a steep increase in molecular weight and width in molecular weight distribution. As the polymerization proceeded, the polymer composition gradually approached the feed composition, identifying the obtained branched copolymer provided some gradients are in its primary chains. Finally, branched copolymer bearing about six primary chains was prepared at monomer conversion near to 80%, its absolute weight average molecular weight was about 8.87 × 10⁴.     

Polystyrenes of known structure: Part 3. Polymers with long-chain branching

The melt- and solution viscosity behaviour of some polystyrenes with long-chain branching is described. These polymers, which were prepared by reacting chloromethylated polystyrene with potassium polystyryl, are distinguishable from the comb-shaped polystyrenes previously described in having longer branches and lower branching frequencies. (The number-average molecular weight of the branches is greater than 4.6 × 10⁴ and in some cases greater than that of the backbone.) Their low shear melt viscosities and intrinsic viscosities in tetrahydrofuran and cyclohexane are above those of the backbone polymer and increase as the branch length increases for a given branching frequency, the rate of increase being greater the lower the branching frequency. In each solvent the intrinsic viscosities of the branched polymers are below those of linear polymers of comparable molecular weights. The melt viscosities of the majority of the branched polymers are also below those of linear polymers of the same molecular weights, but for a few, those with the longest branches in the series with the lowest branching frequency, the opposite is true.     

Dilute solution properties of hydroxyethyl starch

The dilute solution properties of hydroxyethyl starch (HES) were examined by using the techniques of osmometry, light scattering, and viscometry. The molecular weight range was approximately 2 × 10⁶–0.06 × 10⁶. Since HES is a branched molecule, its properties were compared with those of two linear counterparts, ethyl hydroxyethyl cellulose and hydroxyethyl cellulose. The branching index g was estimated to be about 0.3 when calculated from the intrinsic viscosity, radii of gyration, and second virial coefficients.     

Unperturbed dimensions and the g factor of a star-shaped polystyrene

Unperturbed dimensions of a star-shaped polystyrene near the θ temperatures, 25°C, 35°C and 45°C were determined by the measurement of intrinsic viscosity of the polymer in poor solvents. It was found that the inferred mean square radius of gyration of the star-shaped polystyrene, while much smaller than that of the linear polystyrene, as expected, changes much faster with the increase of temperature. The geometric factor g of the star-shaped polystyrene was found to be temperature-dependent.     

Synthesis and characterization of high‐density polypropylene‐grafted polyethylene via a macromolecular reaction and its rheological behavior

High‐density polyethylene grafted isotactic polypropylene (PP‐g‐HDPE) was prepared by the imidization reaction between maleic anhydride grafted polyethylene and amine‐grafted polypropylene in a xylene solution. The branch density was adjusted by changes in the molar ratio between maleic anhydride and primary amine groups. Dynamic rheology tests were conducted to compare the rheological properties of linear polyolefins and long‐chain‐branched polyolefins. The effects of the density of long‐chain branches on the rheological properties were also investigated. It was found that long‐chain‐branched hybrid polyolefins had a higher storage modulus at a low frequency, a higher zero shear viscosity, a reduced phase angle, enhanced shear sensitivities, and a longer relaxation time. As the branch density was increased, the characteristics of the long‐chain‐branched structure became profounder. The flow activation energy of PP‐g‐HDPE was lower than that of neat maleic anhydride grafted polypropylene (PP‐g‐MAH) because of the lower flow activation energy of maleic anhydride grafted high‐density polyethylene (HDPE‐g‐MAH). However, the flow activation energy of PP‐g‐HDPE was higher than that of PP‐g‐MAH/HDPE‐g‐MAH blends because of the presence of long‐chain branches. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Unperturbed dimensions of branched chain,star and ring polymers

A novel Monte Carlo method has been applied to the calculation of the unperturbed dimensions of various monodisperse polymers, e.g. star polymers, branched polymers formed by the crosslinking of linear primary chains, and linear chains with some intramolecular cycles. Where results for the parameters h^?1 and g (representing the effect of branching upon the hydrodynamic radius and the radius of gyration, respectively) were known previously, agreement is good. The method can, however, be applied to furnish other statistical averages for polymers of any arbitrary branched structure, and the effects of polydispersity may also be included.