Do I need to remove the inhibitor before polymerising?

It depends on the level and on the initiator concentration. At low inhibitor levels an excess of initiator will consume it, at the cost of an induction period and some loss of control over molecular weight. For controlled or living polymerisations, removal — by column, distillation or washing — is usually necessary. Knowing the inhibitor level is what lets you decide; it is on the certificate.

Can monomers be supplied uninhibited?

For some, yes, but the shelf life shortens dramatically and storage becomes the buyer's problem — refrigerated, dark, and used quickly. Uninhibited monomer that polymerises in a sealed drum is both a lost material and a genuine hazard, since the reaction is exothermic. Unless the process requires it, taking inhibited material and removing the inhibitor at the point of use is the safer arrangement.

How do I choose between initiators?

Primarily by the ten-hour half-life temperature relative to your process temperature — you want decomposition fast enough to initiate and slow enough to control across the run. Then by solubility in your system, and by whether the decomposition products are acceptable in the product. Two initiators with similar half-lives can still differ in the residues they leave behind.

Polymer Science — Monomers, Initiators & Polymer Intermediates

Specifying it

What decides the purchase

The compound is usually fixed by the route. These are the things that vary between suppliers and between lots.

Inhibitor level is a specification, not a contaminant
Monomers ship with an inhibitor — commonly MEHQ or hydroquinone at tens to hundreds of ppm — to stop them polymerising in storage. It is deliberate. But it also inhibits your polymerisation, so it has to be removed or overcome, and how much is present decides which. State the inhibitor and level you want rather than accepting the default, and never order uninhibited material without a storage plan for it.
Initiators are chosen by half-life at your temperature
A peroxide or azo initiator is characterised by the temperature at which its half-life is ten hours, and that number decides whether it will initiate usefully at your process temperature or decompose too fast to control. Selecting by familiarity rather than by half-life is how a polymerisation runs away or fails to start. It is also why several initiators require refrigerated storage and controlled shipping.
Molecular weight distribution, not just molecular weight
For a supplied polymer or oligomer, an average molecular weight without a dispersity figure describes very little — two materials with the same Mn and different Đ behave differently in viscosity, solubility and mechanical properties. Ask for Mn, Mw and the dispersity, with the method, rather than a single average.
Temperature and time in transit are part of the purchase
Inhibited monomer has a shelf life that assumes a storage temperature, and a container that has spent a summer week in an unrefrigerated warehouse has consumed part of it. For temperature-sensitive initiators the risk is sharper still. Agree the shipping condition and confirm the receiving site can store it correctly before the order is placed.

Questions

Do I need to remove the inhibitor before polymerising?: It depends on the level and on the initiator concentration. At low inhibitor levels an excess of initiator will consume it, at the cost of an induction period and some loss of control over molecular weight. For controlled or living polymerisations, removal — by column, distillation or washing — is usually necessary. Knowing the inhibitor level is what lets you decide; it is on the certificate.
Can monomers be supplied uninhibited?: For some, yes, but the shelf life shortens dramatically and storage becomes the buyer's problem — refrigerated, dark, and used quickly. Uninhibited monomer that polymerises in a sealed drum is both a lost material and a genuine hazard, since the reaction is exothermic. Unless the process requires it, taking inhibited material and removing the inhibitor at the point of use is the safer arrangement.
How do I choose between initiators?: Primarily by the ten-hour half-life temperature relative to your process temperature — you want decomposition fast enough to initiate and slow enough to control across the run. Then by solubility in your system, and by whether the decomposition products are acceptable in the product. Two initiators with similar half-lives can still differ in the residues they leave behind.

Polymer Science

What decides the purchase

Inhibitor level is a specification, not a contaminant

Initiators are chosen by half-life at your temperature

Molecular weight distribution, not just molecular weight

Temperature and time in transit are part of the purchase