Molecular weight, glass transition temperature varying with

Other Properties. The glass-transition temperature for PPO is 190 K and varies htde with molecular weight (182). The temperature dependence of the diffusion coefficient of PPO in the undiluted state has been measured (182). 

The glass transition temperature of a polymer varies with the molecular weight. A low molecular weight component decreases the glass temperature. Its removal by fractionation raises the glass temperature. The present mixing process might cause such a fractionation. Expressed mathematically (127, 128) ... 

The glass transition temperature is dependent on the structure of the polymer, and for the same polymer varies as a function of the polymer molecular weight. The increase in the molecular weight of the polymer is associated, as expected, with an increase in the... 

Relationship Between Molecular Structure and Composition of Poly(ethylene-co-p-MS) Copolymers. From above discussion, we have shown that poly(ethylene-co-p-MS) copolymers with a wide range of compositions can be achieved by varying the p-MS monomer concentration in the feed. To fully understand the properties of this new class of materials, it is very important to know the correlation between the copolymer compositions and their molecular structures. In this section, we focus on the effect of p-MS concentration on molecular weight, molecular weight distribution, melting point (Tm), crystallinity and glass transition temperature (Tg) of the copolymer. A series of copolymers with various p-MS concentrations were analyzed by GPC and DSC. 

Solid-state forming basically uses a male metal plug mold that matches a female metal cavity mold and can be used only with crystalline-type resins. Below their glass transition temperatures Tg) amorphous-type resins are generally too stiff to be rapidly formed into stable products. Crystalline types can be permanently deformed at temperatures between their Tg and melting point (Chapter 1). Molecular orientation, the mechanism that allows this to occur, relates to the draw ratio. Draw ratios can vary from 5 1 for PET and nylon to 10 1 for low molecular weight PP. 

In order to study elastomeric networks, simulating the type of polymers used for tires, we switched to polymers with low glass transition temperatures and oligoether bis-maleimides. A typical random copolymer structure, built from the radical copolymerization of n-hexyl acrylate and 2-furfuryl methacrylate, is shown below. These reactions were conducted in toluene at 80°C with AIBN as initiator. After 8 h, the copolymers were recovered by precipitation in 70 to 80% yields. The compositions varied fi om 2 to 30% of the furanic monomer (monomer feed and copolymer composition were always very similar, suggesting that ri and ti must have both been close to unity). The corresponding Tgs went from -70 to 30°C for molecular weights of about 20,000. Both homopolymers were also prepared as reference materials. 

Hyperbranched polyethers can be synthesized via the A2+B3 approach, when diepoxides (3-24) are reacted with triols, such as TMP. Emrick et al. used 1,2,7,8-diepoxyoctane as the A2 monomer and TMP as the B3 monomer with tetra-n-butylam-monium chloride as the nucleophilic catalyst. Nucleophilic attack of the chloride ion on an epoxide at the less-hindered terminal carbon led to the formation of secondary alkoxide. Due to the equilibrium between primary and secondary alk-oxides via proton exchange, nucleophilic attack of primary alkoxides on the epoxide rings resulted in the formation of aliphatic hyperbranched polyether. As the feed ratio of the diepoxide and TMP was varied from 1.5 to 3, the resulting hb polyether contained two types of terminal units (T), one type of dendritic unit (D), and linear units (L) as shown in Scheme 4. The polydispersity index (PDI) of the polyether increased with the increase of molecular weight (from 1.5-1.8 at M = 1000 up to 5.0 at Mw = 7000). The products are viscous liquids with glass transition temperatures below room temperature. 

---