Free-radical grafting of monomers to polydienes. II. Kinetics and mechanism of styrene grafting to polybutadiene

A kinetic analysis of the grafting reaction has shown that, provided rubber radicals are not involved in termination reactions, the observed normal kinetics of styrene polymerization are to be expected. An expression relating the graft fraction with the rubber and monomer concentrations has been derived and its validity verified from the results reported in Part I. The observation that the molecular weight of the ungrafted PBD falls during the reaction has been explained on a theoretical basis.     

Fundamental studies of grafting reactions in free radical copolymerization. III. Grafting of styrene,acrylate, and methacrylate monomers onto cis-polybutadiene using benzoyl peroxide initiator in solution polymerization

Benzoyl peroxide (BPO), due to its higher radical reactivity as compared to AIBN, is known to promote grafting onto cis-polybutadiene. Switching from AIBN to BPO initiator made a dramatic difference in the extent of grafting for styrene and methacrylate monomers, but only a modest difference for acrylate monomer. For styrene and methacrylate monomers, graft site formation is due to BPO initiator radical attack onto the backbone via allylic hydrogen abstraction. Significant levels of grafting are achieved and depend upon the relative concentrations of monomer and backbone polymer but not upon the level of initiator. For acrylic monomer, graft site formation was found to be due to polymer radical attack at the double bond in the backbone. Abstraction of allylic hydrogen also occurs but results in retardation of the overall reaction rate. Graft level was dependent upon initiator and back-bone polymer concentrations but not upon monomer concentration. The effective role of the initiator is only to produce polymer radicals; the BPO has no direct role in the formation of effective graft sites. © 1995 John Wiley & Sons, Inc.     

甲基丙烯酸缩水甘油酯/苯乙烯固相接枝聚丙烯

以苯乙烯(St)为共单体，过氧化苯甲酰(BPO)为引发剂，采用固相接枝反应将甲基丙烯酸缩水甘油酯(GMA)接枝到聚丙烯(PP)大分子链上。研究了反应时间、单体用量、引发剂用量等因素对接枝率的影响。采用凝胶渗透色谱(GPE)测定了PP和接枝物PP-g-(GMA-St)的分子量和分子量分布。结果 表明固相接枝PP反应条件为[GMA／[St]=2，反应3．5h，加入GMA 10份，BPO 5份。St的加入有助于GMA与PP的接枝，同时在一定程度上抑制了PP的降解。     

Free radical grafting of monomers to polydienes. IV. Kinetics and mechanism of methyl methacrylate grafting to polybutadiene

The radical grafting of methyl methacrylate (MMA) onto polybutadiene (PBD) in benzene solution at 60°C is more efficiently induced by benzoyl peroxide (BP) than by azoisobutyronitrile (AIBN). PBD exerts a pronounced retardation on the polymerization of MMA and the grafting efficiency is governed by the ratio of rubber to monomer in the system. With BP as initiator, a fairly simple kinetic expression, relating grafting efficiency with reactant concentrations, can be derived by making certain approximations, including the neglect of termination grafting. The experimental data are reasonably consistent with this equation and yield acceptable values of several kinetic parameters. With AIBN, termination grafting is more significant. In consequence the relevant kinetic equation can be only qualitatively validated.     

Fundamental studies of grafting reactions in free radical copolymerization. IV. Grafting of styrene,acrylate, and methacrylate monomers onto vinyl-polybutadiene using benzoyl peroxide and AIBN initiators in solution polymerization.

Vinyl-1,2 polybutadiene (vinyl-PBD) was used as the backbone polymer for the grafting of styrene, methacrylate, and acrylate monomers using both benzoyl peroxide and AIBN initiators. Radical attack on the backbone can occur through the pendant vinyl group or at the tertiary, allylic hydrogen site. Effective graft sites are formed via double bond addition of either primary (initiator) or polymer radicals. The production of tertiary allylic radicals on the backbone chain also occurs and results in moderate to dramatic reaction rate re-tardation in every monomer system. The type of initiator is only important when the polymer radicals are not very reactive, as in the case of styrene, and to a lesser extent for methacrylate monomer. Graft efficiencies are generally higher when using vinyl-PBD than when using cis-PBD. © 1995 John Wiley & Sons, Inc.     

Radiation-induced grafting of styrene vapor to polyethylene

The radiation-induced grafting of styrene vapor to low-density polyethylene film of 0.063 mm thickness was studied at 23°C at a dose rate of 1.98 × 10⁴ rad/hr. The concentration C of monomer in the film was measured as a function of pre-irradiation exposure time to monomer vapor. The concentration-dependent diffusion coefficient of styrene in polyethylene was calculated to be 4.9 × 10^?9 exp {2.0C/C₀} cm²/sec, where C₀ is the saturation concentration of styrene in the film, and a linear boundary diffusion coefficient for styrene vapor into polyethylene film was found to be 2.0 × 10^?7 cm/sec. The rate of grafting was determined as a function of the concentration of styrene absorbed in the film. The maximum graft yield was obtained with an initial styrene concentration in the film of 4 wt-%. Under conditions of low initial monomer concentration, the grafting rate increases with irradiation time. The results are compared with previously published data on grafting of polyethylene from methanol–styrene solutions. They are explained in terms of the viscosity of the amorphous region as a function of styrene content and the resistance to the diffusion of monomer at the film–vapor interface.     

Dual monomer grafting of styrene and maleic anhydride onto model hydrocarbon substrates

Styrene and maleic anhydride (MAn) were successfully grafted, alone and simultaneously, onto various model hydrocarbon substrates at 180 °C with 2,5‐dimethyl‐2,5‐di‐(t‐butyl peroxy)hexane (L101) as a free‐radical initiator. Dodecane, 1‐dodecene, and 2,6,10,14‐tetramethylpentadecane were selected as model compounds to investigate the effects of terminal unsaturation and branching on grafting and crosslinking. These compounds were chosen to mimic the aforementioned microstructural characteristics that are commonly observed in polyethylene. The results demonstrate that terminal unsaturation increases the amount of crosslinked material in the presence of L101. With respect to grafting, for the single monomer systems, MAn prefers to graft as single saturated units, whereas styrene prefers to graft as long chains of polystyrene oligomers. However, when both monomers are grafted simultaneously, graft yields are drastically reduced because of a propensity for the two monomers to form a styrene–maleic anhydride copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2456–2468, 2000     

Hydroxypropyl cellulose (HPC)-stabilized dispersion polymerization of styrene in polar solvents: Effect of reaction parameters

Dispersion polymerization of styrene in polar solvents in the presence of hydroxypropyl cellulose (HPC) produces latex particles from ca. 1 to 26 μm depending on reaction parameters. Increasing the initiator concentration or temperature decreases the molecular weight, but increases the particle size and breadth of the size distribution. The decrease in molecular weight with increasing R_i, caused by larger initiator concentration or higher temperature, is expected based of fundamental kinetic relationships. The inverse correlation between size and rate of initiation is rationalized by polarity (stabilizing ability) of the grafted HPC-polystyrene formed in situ. High polar HPC-g-PS, which contains shorter graft polystyrene chain, stabilizes particles less effectively and this leads to larger particles. The primary influence of initial styrene concentration is a solvent effect: larger particles are obtained at high styrene concentration due to high solubility of polystyrene during the initial part of the reaction. The influence of the molecular weight of HPC is to change the polarity of the HPC-g-PS stabilizer. Comparison of particle growth of three critical polymerization systems suggests that the favorable continuous-phase solubility parameter for dispersion polymerization of styrene is around 11.6 (cal/mL)^1/2. Too high or too low polarity generates particles with broad size distribution because large particles are formed during the initial stage and nucleation continues as the polymerization proceeds. © 1992 John Wiley & Sons, Inc.     

Graft copolymerization onto rubber. V. Graft copolymerization of methyl methacrylate onto rubber using potassium peroxydiphosphate as initiator

The graft copolymerization of methyl methacrylate onto natural rubber (NR) is investigated using potassium peroxydiphosphate as the initiator. The rate of grafting is determined by varying monomer concentration, peroxydiphosphate concentration, and temperature. The graft yield increased with an increase in monomer concentration up to 1.4082M/L and thereafter the graft yield decreases. The graft yield increases significantly with an increase of peroxydiphosphate concentration up to 150 X 10^-1M/L and thereafter the graft yield decreases. The grafting reaction is temperature dependent. A suitable kinetic scheme is proposed and the rate equation is evaluated.     

Fundamental studies of grafting reactions in free radical copolymerization. II. Grafting of styrene,acrylate, and methacrylate monomers onto cis-polybutadiene using AIBN initiator in solution polymerization

Grafting can be initiated by primary and/ or polymer radical attack on the backbone polymer and it is well known that AIBN does not readily promote grafting, even when using poly-butadiene. We have studied the grafting of several different monomers onto cis-polybuta-diene using AIBN initiator and find dramatically different results among the monomers. As expected, styrene grafts at very low levels due to the inactivity of the initiator radicals and the polystyryl radicals. Methacrylate monomer grafts at a slightly higher level due to its more reactive polymer radical, while acrylate monomer readily grafts onto the poly-butadiene because polyacrylate radicals are quite reactive. The use of a kinetic model allowed the evaluation of rate coefficients for graft site initiation to be in the relative order of 0.1 : 1.0 : 10.0 (L/mol/s) for styrene:methacrylate:acrylate monomers. The model also pro-vided successful interpretations of the grafting data and its dependence upon the concen-trations of monomer, initiator, and backbone polymer. Due to the relatively higher reactivity of the polyacrylate radicals, the benzene solvent acted as a chain transfer agent in this system. This affected the molecular weight of both free and grafted acrylate polymer and also surpressed the graft level. Polyacrylate radicals attack the cis-polybutadiene backbone by abstracting an allylic hydrogen and also adding across the residual double bond. The latter mechanism is responsible for the majority of the grafting; the hydrogen abstraction leads to relatively inactive radicals which cause a retardation in the overall reaction rate. © 1995 John Wiley & Sons, Inc.     

Grafting Vinyl Monomers onto Silk Fibers. V. Graft Copolymerization of Methyl Methacrylate onto Silk with Potassium Permanganate as Initiator

The graft copolymerization of methyl methacrylate onto silk fibers in aqueous solution with the use of manganese (IV) ions as initiator was investigated. The rate of grafting was determined by varying monomer, acidity of the medium, temperature, nature of silk, and the reaction medium. The graft yield increases significantly with increase of manganese (IV) concentration up to 15 meq/liter; with further increase of manganese (IV) concentration, the graft yield decreases. The effect of the increase of monomer concentration brings about a significant enhancement in the graft yield up to 7%, and with further increase of monomer concentration the graft yield decreases. The graft yield is considerably influenced by chemical modification prior to grafting. The effect of some inorganic salts and anionic surfactants on the rate of grafting has been investigated.     

含氟接枝共聚物为助稳定剂的苯乙烯细乳液聚合反应

以含氟接枝共聚物(PSG)单独作为助稳定剂,十二烷基硫酸钠(SDS)为乳化剂,过硫酸钾(KPS)为引发剂引发苯乙烯(St)的细乳液聚合。考察了聚合温度、乳化剂用量、引发剂用量和PSG用量对细乳液聚合转化率的影响。结果表明,以PSG单独作为助稳定剂,细乳液聚合过程较稳定,起始单体液滴数目与成核粒子数目几乎相等。最终转化率随着乳化剂用量和反应温度的提高而增加,引发剂用量影响不明显。在相同的反应条件下,分别以相同用量(w.t.%=0.091%时,占单体和水的总质量)的PSG和十六醇为助稳定剂用于苯乙烯细乳液聚合,反应290min后,PSG体系的聚合转化率达到87.2%,而十六醇体系的聚合转化率只有78.2%。     

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.     

Grafting vinyl monomers onto silk fibers. IX. Graft copolymerization of methyl methacrylate onto silk using peroxydiphosphate-thiourea redox system

The graft copolymerization of methyl methacrylate (MMA) onto silk in aqueous media initiated by the potassium peroxydiphosphate-thiourea redox system was studied at 50°C. The rate of grafting was determined by changing [monomerl], [thiourea], [initiator], acidity of the medium, reaction medium, and temperature. A significant increase percent of grafting was noticed with increasing monomer concentration to 84.49 × 10^?2 mole/liter and the further increase is associated with the decrease of graft yield. The graft yield increases with an increase of thiourea (Tu) concentration to 25 × 10^?5 mole/liter; then it decreases. A measurable increase in graft yield was observed with an increase in acidity of the medium. Graft yield increases to a certain temperature, i.e., 50°C, and then it decreases. The graft yield increases with an increase of initiator concentration to 60 × 10^?4 mole/liter; then it decreases. The graft yield is medium dependent. A suitable kinetic path has been proposed and the rate equation has been derived.     

Peroxide-Initiated crosslinking of styrene-grafted polymers and copolymers of butadiene

Low molecular weight polymers and copolymers of butadiene were grafted with styrene. The graft products were then crosslinked by using dicumyl peroxide as initiator. The optimum peroxide concentration was established (5 phr). Infrared analysis showed that the reactivity of 1,2-vinyl and that of 1,4-trans double bonds in styrene-grafted polybutadiene is similar. Crosslinking of the graft product seems to involve a radical-chain polymerization of double bonds in the polymer. The reaction rate is proportional to the square root of peroxide concentration and to the concentration of polymer double bonds. Activation energy, reaction heat, reaction order, and crosslinking efficiency were also determined from DSC measurements. No relation was found between the activation energy of crosslinking and the molecular weight of backbone polymer or density of grafting. Crosslinking efficiency was to 25–50 crosslinks per molecule of decomposed peroxide. The crosslinking efficiency for grafted butadiene–styrene copolymers is somewhat lower than that for grafted polybutadienes. From thermogravimetric measurements it was found that the crosslinked grafted polymers show lower resistance to thermal degradation than ungrafted polymers.     

Grafting on polybutadiene with polytetrahydrofuran macroperoxyinitiators. Postpolymerization studies

Grafting reactions of polybutadiene with macro peroxy initiators and postpolymerization were studied. The cationic polymerization of tetrahydrofuran (THF) initiated by the cationic species derived from bis-(4-bromomethylbenzoyl) peroxide (BBP) or bis-(3,5-dibromomethylbenzoyl) peroxide (BDBP) gave the PTHF macroperoxy initiator (MPI). PTHF-b-PMMA macroperoxy initiator (MPIb) was also obtained by the redox polymerization of methyl methacrylate initiated with the hydroxyl ends of PTHF and Ce(IV) salts without decomposing the peroxide groups in the middle. Macroperoxy initiators thermally grafted on cis-polybutadiene (PBD) with thermal curing to yield graft copolymers containing crosslinked and soluble parts, which were separated by the sol-gel analysis. FTIR spectra of the crosslinked samples indicated the characteristic signals of the PTHF, PBD and PMMA blocks. The crosslinked copolymers decomposed at around 470 °C. Postpolymerization of the crosslinked products indicated the increase in crosslinking density which has been followed by measuring the gradual increase of swelling values. Postpolymerization crosslinking was estimated as a first order reaction rate.     

Studies on the grafting of acrylonitrile-co-styrene onto casein

Graft copolymerization of acrylonitrile and styrene mixture was performed on casein in aqueous medium at pH 7.8 using potassium peroxydisulphate as initiator. The effects of monomer concentration, initiator concentration and temperature were investigated. The individual polymers were isolated by Soxhlet extraction and characterized by i.r. spectroscopy and thermogravimetric analysis.     

Mechanism of graft copolymerization of styrene onto deproteinized natural rubber

High conversion and high grafting efficiency attained by graft copolymerization of styrene onto deproteinized natural rubber (DPNR) was investigated with respect to the molecular weight of grafted polystyrene. The graft copolymerization was performed with tert-butyl hydroperoxide/tetraethylenepentamine as an initiator after deproteinization of natural rubber with urea. Grafted polystyrene was isolated from the resulting graft copolymer by ozonolysis reaction. After the ozonolysis of the graft copolymer of DPNR and polystyrene (DPNR-g-PS), the molecular weight of grafted polystyrene was determined by size exclusion chromatography. Effects of initiator and monomer concentrations were investigated with respect to the molecular weight of the grafted polystyrene, which was found to depend on not only the number of active site generated on the rubber particle but also the feed of styrene. Deactivation and chain transfer of the active sites were attributed to effective amount of styrene used for the graft copolymerization.     

Kinetics of radiation-induced grafting reactions. II. Cellulose acetate–styrene systems

Kinetics of grafting reactions of styrene to preirradiated cellulose acetate have been studied by labeling the active sites with bromine atoms. The dilution of styrene monomer with methanol affected grafting reactions remarkedly: e.g., as the concentration of methanol in monomer solutions increased, the growth rates of individual graft radicals decreased while the average lifetimes increased. The integrated amounts of active sites which participated in grafting reactions were also affected by the constitution of monomer solutions and varied roughly in proportion to the extents of swelling of cellulose acetate. Grafting yields for styrene/methanol = 1/1 were higher than for 3/1 and 1/3 throughout the duration of grafting reactions, which is due not only to the high molecular weight of graft chains but also to the large number of graft chains for the 1/1 system compared to the other systems.     

Polymers from renewable resources. II. A study in the radio chemical grafting of poly(styrene‐alt‐maleic anhydride) onto cellulose extracted from pine needles

A binary mixture of styrene and maleic anhydride has been graft copolymerized onto cellulose extracted from Pinus roxburghii needles. The reaction was initiated with gamma rays in air by the simultaneous irradiation method. Graft copolymerization was studied under optimum conditions of total dose of radiation, amount of water, and molar concentration previously worked out for grafting styrene onto cellulose. Percentage of total conversion (Pg), grafting efficiency (%), percentage of grafting (Pg), and rates of polymerization (R_p), grafting (R_g), and homopolymerization (R_h) have been determined as a function of maleic anhydride concentration. The high degree of kinetic regularity and the linear dependence of the rate of polymerization on maleic anhydride concentration, along with the low and nearly constant rate of homopolymerization suggest that the monomers first form a complexomer which then polymerizes to form grafted chains with an alternating sequence. Grafting parameters and reaction rates achieve maximum values when the molar ratio of styrene to maleic anhydride is 1 : 1. Further evidence for the alternating monomer sequence is obtained from quantitatively evaluating the composition of the grafted chains from the FT‐IR spectra, in which the ratio of anhydride absorbance to aromatic (CC) absorbance for the stretching bands assigned to the grafted monomers remained constant and independent of the feed ratio of maleic anhydride to styrene. Thermal behaviour of the graft copolymers revealed that all graft copolymers exhibit single stage decomposition with characteristic transitions at 161–165°C and 290–300°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1763–1769, 1999