1-try reducing speed of monomer addition and 2- reduce Free radical scavenger at the end, and increase polymerization time.

To increase the weight-average molecular weight (Mw) of expanded polystyrene (EPS) produced via free radical suspension polymerization, you can adjust several factors in the polymerization process:

1. Initiator Type and Concentration

• Lower the initiator concentration: A lower initiator concentration reduces the number of free radicals generated, leading to longer polymer chains and higher Mw.
• Use initiators with lower decomposition rates: Slower-decomposing initiators like benzoyl peroxide (at low concentrations) can help produce higher Mw.

2. Monomer Purity and Concentration

• Increase monomer purity: Impurities can act as chain terminators, reducing Mw.
• Use higher monomer concentration: Higher styrene concentrations can result in more efficient propagation relative to termination, increasing Mw.

3. Reaction Temperature

• Optimize reaction temperature: Lower polymerization temperatures reduce the rate of termination (as chain mobility is decreased) and promote longer chains, thereby increasing Mw. However, this can slow down the reaction and may require careful control to avoid incomplete polymerization.

4. Chain Transfer Agent (CTA) Management

• Minimize the use of CTAs: CTAs like mercaptans are often used to control Mw. Reducing their concentration or eliminating them can lead to higher Mw.
• Avoid impurities that act as CTAs.

5. Suspension Stabilizers and Additives

• Use appropriate stabilizers to maintain suspension stability without interfering with radical activity.
• Additives like crosslinking agents (e.g., divinylbenzene in small amounts) can slightly increase Mw by creating a more interconnected network.

6. Polymerization Time

• Extend the reaction time: Longer reaction times allow more propagation to occur, increasing Mw. However, prolonged polymerization can also increase the likelihood of thermal degradation, so careful monitoring is required.

7. Control Oxygen Levels

• Eliminate oxygen from the system: Oxygen acts as a radical scavenger, reducing Mw. Using an inert atmosphere (e.g., nitrogen) can prevent this.

8. Post-polymerization Treatments

• Annealing: Post-polymerization thermal treatments at controlled temperatures can allow further chain growth or reorganization, increasing Mw.

Для увеличения молекулярной массы растворите в мономере полимер перед полимеризацией и за счет гель-эффекта увеличится молекулярная масса. Подробности в моей диссерации.